1. Field of the Invention
The present invention relates to pipeline cleaning systems. More particularly, the present invention relates to tracking systems for pipeline cleaning scrapers which travel inside the pipeline propelled by a cleaning fluid injected at the end of the pipeline.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Scrapers, also known as pigs, are pieces of pipe where elastomer discs are attached radially at various points along the pipe. The elastomer discs of the scraper slide along the internal wall of the pipeline and remove the adhered corrosion and other undesired substances.
Accumulated material adhered on the pipeline internal wall can obstruct passage of the scraper. This produces a stick-slip motion of the scraper in the areas where its mobility is reduced. In some cases, the inside pipeline diameter contour loses circularity, increasing heavily the drag forces acting on the scraper. The scraper reduces speed and is eventually stopped. In other cases, the operating pressure, when launching and pushing the scraper through the pipeline, may drop to undesirable levels at certain points along the pipeline causing the scraper to get stuck or lose momentum. The various changes in scraper speed while it travels along the pipeline make it difficult to detect and locate by pressure monitoring systems, or other flowrate and pressure drop modeling systems.
Various patents have issued in the past relating to pipe scrapers or pigs. For example, U.S. Pat. No. 4,798,246, issued on Jan. 17, 1989 to Best, describes a pipe scraper. The pipe scraper has scraper blades having arcuate scraper surfaces projecting therefrom. The blades are movable radially between a contracted and expanded position which provides a first minimum diameter of the scraper surfaces in contracted position and a second maximum diameter when in expanded position which extends at least to the maximum internal pipe diameter. An adjustment arrangement enables the arcuate scraper blades to be adjusted radially to maintain the first and second diameters as the scraper surfaces wear.
U.S. Pat. No. 5,600,862, issued on Feb. 11, 1997 to Bleske et al., teaches a pipe scraper. The pipe scraper is for removing a uniform amount of material from the perimeter of a pipe. The pipe scraper has a shoulder and biased members for urging the pipe against an interior surface of the scraper body to achieve a uniform scrape with both round and oval pipes, without a need for blade adjustment. Uneven scraping due to canting of the pipe with respect to the body is also eliminated.
U.S. Pat. No. 5,528,790, issued on Jun. 25, 1996 to Curran, describes another pipe scraper assembly. The pipe scraper assembly is forced through condenser pipe interiors for scraping residue off the inner wall surface. The scraper assembly is formed with a cylindrical body with a head and a tail end. Several mutually spaced apart rings are coaxially and rotatably supported on the cylindrical body between the head and the tail end. The diameter of the rings corresponds to the inner diameter of the pipe to be scraped. The rings have a radial cut formed therein which extends obliquely relative to the longitudinal axis of the cylindrical body.
U.S. Pat. No. 5,035,021, issued on Jul. 30, 1991 to Le Devehat, teaches a scraper for liquid distribution pipes, particularly for petroleum products. The pipeline scraper has an elongated body defined by two complementary parts that form end portions and a reduced cross-section central portion, two wear segments surrounding and mounted on the central portion adjacent the end portions, and threaded means releasably fastening the components together.
U.S. Pat. No. 4,677,865, issued on Jul. 7, 1987 to Lehmann, describes a pipe pig with running gear. The pipe pig is supported on and moved by two or three runners, which also can move circumferentially on the inside of the pipe to alter the angular position of the runners with respect to the longitudinal axis of the pipe. In this way the runners, which support the pipe pig by contact with the inside surface of the pipe, may rotate so as to avoid obstructions as they are encountered. Such obstructions may take the forms of openings in the pipe wall or protrusions into the pipe from the pipe wall. Various devices may be used to detect the presence of such obstacles and to detect both the axial position and angular orientation of the pig within the pipe. The apparatus for changing the angular position of the runners may be integrated with or separate from the apparatus for moving the pig axially in the pipe.
U.S. Pat. No. 5,358,573, issued on Oct. 25, 1994 to Sivacoe, describes a method of cleaning a pipe with a cylindrical pipe pig having pins in the central portion. The pipe pig is reciprocated through a section of a pipe having deposits of scale. In the case of very hard deposits, each pass through the contaminated sections removes a thin layer each time. The location of the coated section can be located by first running the pig through the pipe. The hydraulic pressure is monitored using pen recorders. At each bend in the pipe, a sharp pressure increase will be recorded. The location of the bends can be determined from a drawing of the pipe installation. When the pig encounters scale, there will be a pressure increase that corresponds to the degree of resistance met by the pig resulting from the scale. Greater pressure means greater scale buildup. By running the pig through the pipe, a profile of the scale may be created. The location of the scale can be correlated to the known location of the bends. The scale itself can be flushed out with the hydraulic propellant and analyzed. The pin height and hardness can then be selected for the particular scale encountered. The pig may be run backwards and forwards primarily through the contaminated section. After several passes, the pig can be removed from the pipe, the pins replaced or moved radially outward by placing washers between at least some of the pins and the pig body and the pig returned to the pipe.
U.S. Pat. No. 5,685,041, issued on Nov. 11, 1997 to Sivacoe, teaches a pipe pig with an abrasive exterior. Additionally, the patent teaches a method of making a rotationally symmetric pipe pig in which porous abrasive material is adhered to the periphery of the pipe pig. A liquid applied surface layer of the pig body forms an adhesive for the porous abrasive material, which is cured after the application of the porous abrasive material. The porous abrasive material is alumina ceramic beads. The pipe pig thus formed has a porous abrasive material adhered to the periphery of the pipe pig.
Various patents have issued in the past relating to acoustic leak detection in pipelines. Leak detection technology may be used in conjunction with scraper technology of the present invention. One of the present inventors is the inventor of several patents in the field. For example, U.S. Pat. No. 6,389,881 issued on May 21, 2002 to Yang, et al. describes a method and apparatus for pattern match filtering for real time acoustic pipeline leak detection and location. The patent describes how pattern match filtering is used to reduce false alarm rate, increase sensitivity and improve leak location accuracy, while quickly detecting leaks by the acoustic signal generated from a leak event in pipelines containing gas or liquid under pressure. The pattern match filter technique detects a pressure wave generated by a leak, but discriminates against background noise and pressure disturbance generated by other non-leak sources that might otherwise be detected as a leak. The pattern match filter derives a sharp peaked output from the signal of the expansion wave which allows for a distinctive point of reference for a time stamp. This provides for improved accuracy in leak location calculations. The pattern match filter is incorporated into site processors located at multiple points along a pipeline, and at a central node processor which receives data from all site processors, performs further evaluation and identification, as well as scraper position and speed calculation. The pattern match filter includes using previously recorded leak profiles. At site processes located at multiple points along a pipeline, a series of previously recorded signature profiles are continuously compared in real time against pipeline pressure signals. Data from each site processor are used collectively at a node processor and compared against multiple leak profiles to provide further false alarm rejection. The leak event data generated at each site processor is used by the node processor to declare a leak. By the application of this pattern match filter technique, the signal to noise ratio (S/N ratio) required to identify a leak event is reduced and the sensitivity of leak detection is increased. U.S. Pat. No. 6,668,619 issued to Yang et al. on Dec. 30, 2003 describes a related method of pattern match filtering.
The difficulties in determining position and speed of the scraper as it travels along the pipeline reside also on the inherent limitations of radio frequency transmitters in reaching, from the inside of a metallic pipe, a few tens of meters away from the pipe wall. This limitation imposes the need for utilizing multiple signal receivers placed outside the pipe wall at regularly spaced intervals and sufficiently close to the pipeline in order to ensure proper reception of the signal transmitted by the scraper built-in transmitters.
Therefore, what is needed is a system capable of measuring and accurately determining position and speed of the scraper traveling inside a metallic pipe.
It is an object of the present invention to provide a system for tracking scrapers as they move along a pipeline.
It is another object of the present invention to provide a scraper tracking system which utilizes acoustic pressure sensors and data processors.
It is yet another object of the present invention to provide a scraper tracking system which accurately and precisely locates scrapers.
It is another object of the present invention to provide a scraper tracking system which can determine the speed of a scraper moving through a pipeline.
It is a further object of the present invention to provide a scraper tracking system that can be used in conjunction with current acoustic sensor technology.
It is another object of the present invention to provide a scraper tracking system that utilizes pattern recognition techniques such as previously developed pattern techniques described in U.S. Pat. No. 6,668,619, neural network-based approaches, or other methods to identify the unique acoustic pressure wave pattern emitted a signal generator contained within the scraper.
It is yet another object of the present invention to provide a scraper tracking system that utilizes pattern recognition techniques such as previously developed pattern techniques described in U.S. Pat. No. 6,668,619, neural network-based approaches, or other methods to identify the unique local pressure transient profile associated with the passing of the scraper and its incoming and departing dynamics.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.